Our aim is to study the distribution of nicotinic acetylcholine receptors in intact and cultured tissues of the peripheral and central nervous system in relationship to the development and function of synapses. To this purpose histochemical localization of alpha-bungarotoxin bound to the receptors is used in conjunction with light and electron microscopy. In the past year we have studied the ultrastructural distribution of receptors on cultured skeletal muscle fibers and have initiated the following investigations: 1) location and characterization of synapses formed by neuroblastoma hybrid cells in culture 2) modification of histochemical methods in order to permit ultrastructural analysis of receptor distribution in the central nervous system and 3) analysis of the distribution of receptors in the visual system of the goldfish with relationship to optic nerve damage and regeneration.